Phased Array Ultrasonics and Eddy Current Examination for Graphite Components

Transcription

1 Phased Array Ultrasonics and Eddy Current Examination for Graphite Components June 22, th International Symposium on Nondestructive Characterization of Materials Blacksburg, Virginia Tim McJunkin, Dennis C. Kunerth Idaho National Laboratory

2 Overview of Activities Identify nondestructive evaluation (NDE) techniques for graphite Expect material variations within billets, billet to billet and lot to lot Material condition will change with service Need inspection techniques suitable for large billets, fabricated components and in-service inspection Presently evaluating accepted technologies X-ray radiography/tomography (volumetric inspections) Eddy current inspection (surface/near surface inspection) Ultrasonic inspection (volumetric, surface/near surface inspections) Need to implement complementary techniques to provide a more complete understanding of material condition

3 Experiment with Graphite Cylinders Cylinders machined from a block of graphite NGB 18 Cylinders were compressed with various pressures 8 samples from 0 to 70 MPa increments of 10MPa Expecting to see indications of micro-cracking or mechanical changes. NDE Techniques that can observe differences could be used for in service inspection of graphite components

4 NDE Techniques Surface scan with Eddy Current has not shown measurable differences. Sound speed variations are observable. Work in progress on application of acousto-ultrasonic techniques with conventional transducers. Flexibility of phased array ultrasonic are also a work in progress Variations in steering, focus, and choice of aperture can be exploited Developing analysis techniques to find the appropriate statistics to show relative variations. Phased array allow multiple techniques to be applied concurrently.

5 Acoustic Velocity

6 Acousto-Ultrasonics Transmit Receive Test Sample Ultrasonic energy randomly scatters in sample Scatters off grains, pores, cracks, inclusions, etc Character of detected ultrasonic energy determined by scatter and energy dissipation mechanisms Potentially used to detect changes in batch to batch microstructure or microstructural damage 2.25 MHz transducers 15 mm separation

7 Acousto-Ultrasonics Acousto-Ultrasonic Measurements (7 Graphite Test Samples) Signal Amplitude (volts) Time (microseconds)

8 Acousto-Ultrasonics

9 Acousto-Ultrasonics Analysis Sliding Window FFT

10 Acusto-Ultrasonics

11 Acousto-Ultrasonics 10 MPa Stress 70 MPa Stress

12 Acousto-Ultrasonic and Backscatter Techniques With Phased Array Goal: Explore benefits of flexibility of phased array ultrasonics on traditional acousto-ultrasonic and back scatter techniques concurrently with standard UT With separate apertures, steer transmit and receive beams towards each other with different depth crossings to depth profile Use alternating element aperture and variable depth focus for back scatter sensitive at various depths

13 Phased Array Setup 64 Element Linear Array 2.25Mhz 0.7 mm pitch Olympus NDT Focus-LT Tomoview Software INL Custom Focal Laws

14 Phased Array Managing Many Inspection Methods Concurrently

15 Details of AU with Steering Trx Rcx

16 Phased Array Back Scatter

17 Details of Backscatter Varying Depth Of Focus Alternate elements Transmit/Receive

18 AU samples at various compression No Compression Highest Compression Greater returns from back angle focal laws

19 Back Scatter Elimination of indication allow for statistical variations between compression levels. But so far only small variability with current samples. Low Compression Medium Compression Highest Compression

20 Eddy Current Inspection Flat bottom holes 2.4 mm 1.6 mm 0.8 mm Notch 0.25 x 0.25 mm Inspections based on electromagnetic properties of test material Surface/near surface inspection due to skin effect and limited projection of magnetic field Transverse C-Scan Axial C-Scan

21 Eddy Current Inspection Pulse Eddy Current Image X-Ray Image

22 Challenges and Barriers Sample sets with controlled microstructural features and known defects Porosity Cracking Microcracking Oxidation Ultrasonic coupling Test surface condition Statistics from new methods to compile cross-section or volumes of data.

23 Summary At current compression levels very subtle variations are found in the AU and back scatter using the traditional and new techniques. Flexibility of phased array can be further exploited to better determine signatures of materials. Working to arrive at a better set of samples to test the examination techniques.

24 Dennis C. Kunerth Idaho National Laboratory (208) Timothy R. McJunkin Idaho National Laboratory (208)

25 X-Ray Radiography/Tomography Inspections based on attenuation of x-rays propagating Through a test sample 2D projection radiograph 159 x 165 mm graphite blocks

26 X-Ray Radiography/Tomography 152 mm dia. graphite cylinder 1, 2, 4, 6, and 8 mm dia. drill holes

27 Eddy Current Inspection Pulse Eddy Current Images

28 Ultrasonic Inspection Inspections based on elastic properties of test material and scattering of propagating acoustic wave Graphite attenuates high test frequencies Test frequencies 1 Mhz have wavelengths >2 mm Limited capability for detection of small isolated defects Velocity and scattering measurements

29 Ultrasonic Inspection (Acoustic Velocity) Signal Amplitude Signal Time of Flight 2.25 MHz 0.5 MHz